The ensemble optical/ultraviolet variability of narrow-line Seyfert 1 (NLS1) type active galactic nuclei (AGNs) is investigated, based on a sample selected from the Sloan Digital Sky Survey (SDSS) Stripe-82 region with multi-epoch photometric scannin
g data. As a comparison a control sample of broad-line Seyfert 1 (BLS1) type AGNs is also incorporated. To quantify properly the intrinsic variation amplitudes and their uncertainties, a novel method of parametric maximum-likelihood is introduced, that has, as we argued, certain virtues over previously used methods. The majority of NLS1-type AGNs exhibit significant variability on timescales from about ten days to a few years with, however, on average smaller amplitudes compared to BLS1-type AGNs. About 20 NLS1- type AGNs showing relatively large variations are presented, that may deserve future monitoring observations, for instance, reverberation mapping. The averaged structure functions of variability, constructed using the same maximumlikelihood method, show remarkable similarity in shape for the two types of AGNs on timescales longer than about 10 days, which can be approximated by a power-law or an exponential function. This, along with other similar properties, such as the wavelength-dependent variability, are indicative of a common dominant mechanism responsible for the long-term optical/UV variability of both NLS1- and BLS1-type AGNs. Towards the short timescales, however, there is tentative evidence that the structure function of NLS1-type AGNs continues declining, whereas that of BLS1-type AGNs flattens with some residual variability on timescales of days. If this can be confirmed, it may suggest that an alternative mechanism, such as X-ray reprocessing, starts to become dominating in BLS1-type AGNs, but not in NLS1-, on such timescales.
The optical variability of 29 flat spectrum radio quasars in SDSS Stripe 82 region are investigated by using DR7 released multi-epoch data. All FSRQs show variations with overall amplitude ranging from 0.24 mag to 3.46 mag in different sources. About
half of FSRQs show a bluer-when-brighter trend, which is commonly observed for blazars. However, only one source shows a redder-when-brighter trend, which implies it is rare in FSRQs. In this source, the thermal emission may likely be responsible for the spectral behavior.
Narrow-line Seyfert,1 galaxies (NLS1s) with very small broad-line widths (say, FWHM(hb) $la $ 1200,kms) represent the extreme type of Seyfert,1 galaxies that have small black hole masses (mbh) and/or high Eddington ratios (redd). Here we study the X-
ray properties of a homogeneously and optically selected sample of 13 such objects, termed as very narrow line Seyfert,1 galaxies (VNLS1s), using archival xmm data. It is found that the Fe K$alpha$ emission line is at most weak in these objects. A soft X-ray excess is ubiquitous, with the thermal temperatures falling within a strict range of 0.1--0.2,keV. Our result highlights the puzzling independence of the thermal temperature by extending the relations to even smaller FWHM(hb), i.e., smaller mbh ($sim 10^6$ msun) and/or higher redd. The excess emission can be modeled by a range of viable models, though the disk reflection and Comptonization models generally give somewhat better fits over the smeared absorption and the $p$-free models. At the Eddington ratios around unity and above, the X-ray spectral slopes in the 2--10,keV band are systematically flatter than the Risaliti et al.s predictions of the relationship with redd suggested previously. Short timescale (1--2 hours) X-ray variability is common, which, together with the variability amplitude computed for some of the objects, are supportive of the scenario that NLS1s are indeed AGN with relatively small mbh.
The dependence of the long-term optical/UV variability on the spectral and the fundamental physical parameters for radio-quiet active galactic nuclei (AGNs) is investigated. The multi-epoch repeated photometric scanning data in the Stripe-82 region o
f the Sloan Digital Sky Survey (SDSS) are exploited for two comparative AGN samples (mostly quasars) selected therein, a broad-line Seyfert,1 (BLS1) type sample and a narrow-line Seyfert,1 (NLS1) type AGN sample within redshifts 0.3--0.8. Their spectral parameters are derived from the SDSS spectroscopic data. It is found that on rest-frame timescales of several years the NLS1-type AGNs show systematically smaller variability compared to the BLS1-type. In fact, the variability amplitude is found to correlate, though only moderately, with the Eigenvector,1 parameters, i.e., the smaller the hb linewidth, the weaker the [O,III] and the stronger the feii emission, the smaller the variability amplitude is. Moreover, an interesting inverse correlation is found between the variability and the Eddington ratio, which is perhaps more fundamental. The previously known dependence of the variability on luminosity is not significant, and that on black hole mass---as claimed in recent papers and also present in our data---fades out when controlling for the Eddington ratio in the correlation analysis, though these may be partly due to the limited ranges of luminosity and black hole mass of our samples. Our result strongly supports that an accretion disk is likely to play a major role in producing the opitcal/UV variability.
